Electrum (the wallet I'm using to store funds) moves all my funds from one address to a brand new one, every time when I send a transaction.
You can actually change the setting which will stop this phenomenon and will keep the unused BTC on the same address...
1. Click the setting button
2. Click the tab Transactions
3. Uncheck the option Use change addresses (here the option is checked though)
Unchecking #3 will always keep the unused bitcoin to it's original wallet.
Hope it helps
